Antenna windows of modern automotive vehicles must satisfy the extreme requirements for the reception and transmission of electromagnetic waves and, indeed are required to act as broad-band antennas, i.e. antennas which are effective over a wide frequency range for electromagnetic waves of different polarizations. The high requirements pertain not only to energy requirements but also to the geometry of the radiation or reception characteristics.
Typical frequency ranges include long wave, middle wave and shortwave ranges and the usual AM range (150 kHz-30 MHz), the VHF range for radio and television reception (30 MHz to 300 MHz) and the UHF range for television reception, for mobile radio and for satellite communication (global positioning satellite--GPS or the like), and remote control devices (300 MHz-2 GHz).
In practice, antenna windows for automotive vehicles have used antenna elements which have the configuration of wires or are conductors which are screen-printed on a glass pane and are burned into the substrate, or are antenna elements formed from electrically-conductive coatings.
Reference may be made specifically to U.S. Pat. No. 5,355,144 and German Patent 37 43 099. If the antenna pane is a safety glass pane having an inner pane, an outer pane and a bonding layer, for the reception and transmission of radio waves, an optically-transparent electrically-conductive coating can be provided. This conductive coating has, once it has been incorporated into the antenna window, a relatively broad peripheral spacing from the edge of the window opening and thus from the metallic body. As a result the metallic layer is electromagnetically decoupled significantly from the body of the vehicle.
The feed to the antenna window and the coupling of radio waves from the latter is effected with the aid of coaxial cables. Research has shown that the transmission and reception characteristics from an energy point of view as well as from the directional characteristic point of view can be improved. This is especially the case when the antenna pane must be satisfactory for transmission and reception in a broad-band range.
Vehicles are also known in which the window is provided with electrically-conductive solar control coatings, for example coatings of noble metal or semiconductive metal oxide. The solar control coating is either applied directly upon the glass panes assembled to form the window or is provided on a thin transparent foil, for example, of polyethyleneterephthalate (PET) which is bonded with bonding layers with the glass panes, especially between the latter. The aforementioned solar control coatings are customarily applied over the entire window area and thus run to all edges of the window pane.
Vehicles are also known in which the window is provided with electrically-conductive solar control coatings, for example coatings of noble metal or semiconductive metal oxide. The solar control coating is either applied directly upon the glass panes assembled to form the window or is provided on a thin transparent foil, for example, of polyethyleneterephthalate (PET) which is bonded with bonding layers with the glass panes, especially between the latter. The aforementioned solar control coatings are customarily applied over the entire window area and thus run to all edges of the window pane.
The solar control coating, in the context of the present invention is intended to refer to all electrically-conductive coatings which can reduce solar energy transmission in at least a partial region of the solar spectrum. Usually the reduction is in the visible and infrared ranges.
For vehicles which have windows with such solar control coatings, it has been difficult, if not impossible, to provide antenna windows with good reception and/or transmission quality over a broad band, without noticeable detriment to the solar control effectiveness or damage to the optical characteristics.